JP2003069523A - Ofdm communication device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an OFDM communication device which improves communication quality and cuts down the waste of sending power based on the CNR estimation concerning with transmission paths such as electric power lines. SOLUTION: The OFDM communication device receives the ODDM signals including preamble signals composed of predetermined fixed data, and then fetches out at least two preamble signals from the received signals to interconnect them so that it generates expanded preamble signals. By transforming the signals into frequency data using Fourier transform means, the device calculates in a lump carrier wave components relating to the expanded preamble signals and the other noise components, and performs the CNR estimation of the carrier wave components based on the result.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an OFDM communication apparatus, and more particularly to a carrier to noise ratio (Carrier to No.
ise Ratio, hereinafter referred to as CNR) to improve communication quality.

[0002]

2. Description of the Related Art In power line communication, information is transmitted using a power line such as an outdoor distribution line or an indoor power line that is provided to supply electric power, and it is necessary to newly lay a communication line. Since it is possible to reduce the cost of communication without
Conventionally, various methods have been studied. While the power line communication has the above advantages, it uses a power line that has poor transmission characteristics due to noise and the like, and thus needs to use a communication system that is resistant to noise.

Orthogonal Frequency Division Multiplexing
y Division Multiplexing (hereinafter referred to as OFDM))
This is a type of multi-carrier modulation method that disperses channel data over multiple carriers and transmits it. Since the data is dispersed over multiple carriers, the probability of all data loss due to noise is low, and therefore communication suitable for power line communication Known as the scheme.

FIG. 7 shows a conventional OFD in a power line communication device.
FIG. 3 is a functional block diagram showing a configuration example of an M communication device. The power line communication device shown in this figure has an OFDM modulator 10 as a transmission system.
0 through the D / A converter (digital / analog converter) 110 and the low-pass filter 120 to the intermediate frequency / high frequency processing unit (hereinafter, I
(Hereinafter referred to as F / RF processing unit) 130, and the IF / RF processing unit 130 as a reception system via an antialiasing filter (low-pass filter) 140 and an A / D converter (analog / digital converter) 150. It is configured by being connected to the OFDM demodulation unit 200.

Since the OFDM system is described in detail in, for example, "Makoto Itami, OFDM Modulation Technique, Trikeps, March 2000", etc., only the essential points will be described here. OF
The DM modulation unit 100 is a symbol mapper 101 that generates a predetermined modulated signal by dispersing transmission data into a plurality of orthogonal carrier waves with each frequency component partially overlapping, and S / that converts serial data into parallel data. P conversion circuit 102 and an inverse fast Fourier transformer (Inverse Fas
t Fourier Transform (hereinafter referred to as IFFT) 103, and a P / S conversion circuit 104 for converting parallel data into serial data
And a transmission side guard interval circuit 105 for reducing the influence of multipath due to the reflected wave from the transmission path (power line) branch are sequentially connected.

Further, since the OFDM demodulation section 200 obtains a demodulated signal by the reverse operation of the OFDM modulation section 100 described above, the reception side guard interval circuit 201, the S / P conversion circuit 202 and the reception O
Fast Fourier Transform (Fast Fourier Transform) as a Fourier transform means for generating the plurality of orthogonal carrier waves from the FDM signal.
A Fourier Transform (hereinafter referred to as FFT) 203, a P / S conversion circuit 204, and a symbol demapper 205 that performs a predetermined demodulation process are sequentially connected and configured.

FIG. 8 is a diagram showing a spectrum of a signal output from the symbol mapper 101. This example shows a spectrum in the case of generating an OFDM signal using n carriers, and each spectrum is arranged so as to overlap a part of an adjacent spectrum in order to improve frequency utilization efficiency.

FIG. 9 is a diagram showing an example of an OFDM signal (a signal in which 16 carrier waves are multiplexed) output from the transmitting side P / S conversion circuit 104 when 16 carrier waves (n = 15) are used. Is.

The operation of the OFDM communication apparatus shown in FIG. 7 will be described below with reference to FIGS. 8 and 9 including the operation of the entire power line communication apparatus. First, as the operation of the transmission system,
The symbol mapper 101 transmits the transmission data to a plurality of carriers that have frequency components as shown in FIG. 8 and are orthogonal to each other, and a predetermined modulated signal (for example, quadrature amplitude modulation (QAM), or,
When phase modulation (PSK) is generated and output, the S / P conversion circuit 102 converts this to a parallel signal.

Although accurate orthogonality is not guaranteed for this modulated signal due to the shift of the generation timing (phase shift) of each carrier, each carrier is converted into a signal in the time domain by the IFFT converter 103. It is known that the above deviation of the generation timing can be corrected by
The signal is output as a multiplexed waveform as shown in FIG. This OFDM signal is returned to a serial signal by the P / S conversion circuit 104, processed into a signal that is less susceptible to multipath by the transmission side guard interval circuit 105, and the D / A converter 110 and the low-pass filter 120. Converted to an analog signal with harmonics removed via the IF / RF processing unit 1
After a predetermined process is performed in 30, the data is sent to the transmission path.

On the other hand, as the operation of the receiving system, the IF / RF processing unit 1
When the OFDM signal converted into a digital signal by removing unnecessary waves after the predetermined processing is input to the OFDM demodulation unit 200 via 30 and the anti-aliasing filter 140 and the A / D converter 150,
The guard interval processing on the transmission side is canceled by the guard interval circuit on the reception side 201, converted into a parallel signal in the S / P conversion circuit 202, and supplied to the FFT 203. FFT203
Generates a plurality of orthogonal carrier waves (modulated signals) from this signal as frequency components, and supplies this to the symbol demapper 205 via the P / S converter 204, where the transmission data is reproduced from the modulated signals. In order to do so, a predetermined demodulation process is performed.

As shown in FIG. 8, since a part of the spectrum of each carrier in the OFDM signal overlaps the adjacent spectrum, each carrier cannot be extracted (separated) by a filter. However, as is well known, it is possible to separate signals by utilizing the orthogonality between carrier waves.
Since the description of this is complicated, explanation is omitted.
(It is described in pp.37-41 of the above document).

As described above, since an OFDM signal transmits one channel signal using a plurality of carriers, even if the data of a specific carrier is lost due to noise, there is a low possibility that the data of the entire carrier will be lost. Therefore, the information data can be transmitted and received even when the power line is used as a transmission line by using a predetermined error correction technique together.

[0014]

The conventional multicarrier communication device (OFDM communication device) as described above has the following problems. In other words, for the power line used as a transmission line, the type of electronic device connected to it,
Noise with varying levels and frequency distributions is generated depending on the number of connections, usage conditions, and power line installation conditions. Therefore, while a carrier using a frequency with a high CNR characteristic (low noise level) can realize good communication with few information transmission errors, a carrier using a frequency with a low CNR characteristic (high noise level) can generate information due to noise. There was a problem that communication quality deteriorates due to frequent transmission errors. In addition, in the worst case, communication becomes impossible, and there is a problem that transmission power is wasted. To solve such a problem, Japanese Patent Laid-Open No. 2000-165304 discloses a power line communication apparatus using a multi-carrier method, in which a transmission method or a modulation method with a higher transmission rate with respect to a received SNR (CNR) is selected, or a carrier is selected. There is a description regarding the selection of. Further, Japanese Patent Laid-Open No. 2000-216752 describes that in a multicarrier communication device, only carriers other than the band in which the influence of noise is large are used. However, the above publication does not disclose any specific noise evaluation means or CNR evaluation means relating to these devices (transmission paths). The applicant of the present application, in Japanese Patent Application No. 2001-125916 filed on April 24, 2001, samples a large number of received signals at the output of the Fourier transform means to obtain an average signal.
(S) and the noise power (N) from the dispersion characteristics of the noise component to obtain SN
We propose a power line communication device for R (CNR) estimation. However, in order to shorten the processing time, a more efficient CNR estimation means has been required.

The present invention has been made in order to solve the above-mentioned problems relating to the conventional multi-carrier communication device (OFDM communication device), and OFDM communication having means for efficiently performing CNR estimation related to a transmission line such as a power line. The purpose is to provide a device.

[0016]

In order to achieve the above object, the invention according to claim 1 of the OFDM communication apparatus according to the present invention is an OFDM having a plurality of preamble signals composed of predetermined fixed data. While receiving the signal,
At least two or more of the preamble signals are extracted from this received signal and combined to generate an extended preamble signal, which is converted into frequency data by using a Fourier transform means, and a carrier component related to the extended preamble signal and Noise components other than the above are collectively calculated, and the CNR of the carrier component is estimated based on this result. The invention according to claim 2 of the OFDM communication apparatus according to the present invention, at least as a transmission system, disperses transmission data into a plurality of orthogonal carrier waves with each frequency component partially overlapping, and a predetermined target based on a plurality of modulation schemes. A symbol mapper for generating a modulated signal, and an inverse Fourier transform means for multiplexing the modulated signal in the time domain and outputting an OFDM signal, and a Fourier system for generating a plurality of orthogonal carrier waves from a received OFDM signal as a reception system. An OFDM communication device comprising a conversion means and a symbol demapper for performing a predetermined demodulation process, wherein the received OFDM signal has a plurality of preamble signals composed of predetermined fixed data, and the preamble signal. To extract and concatenate at least two of them to generate an extended preamble signal, which is transformed into frequency data using Fourier transform means. By doing so, the carrier component related to the extended preamble signal and the noise component other than that are collectively calculated, and the CNR of the carrier component is estimated based on the result. The invention according to claim 3 of the OFDM communication device according to the present invention is the OFDM communication device according to claim 2, wherein transmission data is transmitted from the plurality of modulation methods for each carrier based on the CNR value obtained by the CNR estimation. Communication control is performed to select the modulation method that optimizes the rate. OF according to the present invention
The invention according to claim 4 of the DM communication device, in the OFDM communication device according to claim 2 or claim 3, the communication control so as not to use the carrier when the CNR value obtained by the CNR estimation is lower than a predetermined value. I decided to do it. . Related to the invention
The invention according to claim 5 of the OFDM communication device, claims 1,
2, In the OFDM communication device according to claim 3 or 4, the plurality of preamble signals are continuous for a predetermined number, and at least two or more of these are taken out as continuous preamble signals.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail below based on the illustrated embodiments. The OFDM communication device according to the present invention is a power line communication device that is a wired communication system, or
Although it can be used for both fixed and mobile wireless communication devices, a case where it is used for a power line communication device will be described as an example. FIG. 1 is a functional block diagram showing an embodiment example in which the OFDM communication apparatus according to the present invention is used in a power line communication apparatus. The feature of the present invention is that the CNR described later in the receiving system.
First, the configuration of the entire apparatus will be described, although it has an estimating means. The power line communication device shown in this example has an OFDM modulation unit 10 as a transmission system via an D / A converter (digital / analog converter) 30 and a low-pass filter 40 at an intermediate frequency /
A high-frequency processing unit (hereinafter referred to as an IF / RF processing unit) 50 is connected to the IF / RF processing unit 50 as a receiving system, an anti-alias filter (low-pass filter) 60 and an A / D converter (analog / digital converter). ) 70 and is connected to the OFDM demodulation unit 20.

The OFDM modulation section 10 distributes the transmission data to a plurality of orthogonal carrier waves with each frequency component partially overlapping and generates a predetermined modulated signal from a plurality of modulation systems, and serial data. Convert to parallel data
S / P conversion circuit 12 and an Inverse Fast Fourier Transform (IFF) as an inverse Fourier transform means.
13), a P / S conversion circuit 14 for converting parallel data to serial data, and a transmission side guard interval circuit 15 for reducing the effect of multipath due to the reflected wave from the transmission path (power line) branch. Connected and configured.

Further, since the OFDM demodulation section 20 obtains a demodulated signal by the inverse operation of the above-mentioned OFDM modulation section 10, the reception side guard interval circuit 21, the S / P conversion circuit 22 and the received OFDM signal are orthogonal to each other. The first fast Fourier transformer (Fast Fourier Transform) as a Fourier transform means for generating a plurality of carrier waves.
Transform, FFT) 23, a P / S conversion circuit 24, and a symbol demapper 25 that performs a predetermined demodulation process are sequentially connected, and a transmission line is provided at a stage subsequent to the guard interval circuit 21.
CNR estimation unit 26 for estimating the CNR characteristics related to (power line)
And a modulation method / carrier control unit 27 for selecting a modulation method in the symbol mapper 11 and the symbol demapper 25 or a carrier to be used based on the estimation result.

The basic operation of the power line communication apparatus including the OFDM modulator / demodulator is the same as that of the above-mentioned conventional technique, and therefore its explanation is omitted.

In the present invention, the CNR estimating unit 26 estimates the CNR characteristics related to the transmission path, and a plurality of modulation methods (for example, PSK / QPSK / 8PSK / 16PS) for each carrier are estimated based on the estimated values.
The symbol mapper 11 and the symbol demapper 25 are controlled via the modulation method / carrier control unit 27 so as to select the optimum method from K).

That is, BPSK (binary PS used as a modulation method
(K) / QPSK (4 level PSK) / 8PSK (8 level PSK) / 16PSK (16 level PSK), the number of information bits that can be transmitted by 1 symbol is 1/2/3 /
It is 4 bits. Here, the more the information bit number can be transmitted, the more the signal interval (PSK
In the system, the phase shift interval) becomes narrower. For example, the phase shift interval of BPSK is 180 °, QPSK is 90 °, and 8PSK is 45 °, so that the more information bits can be transmitted, the more easily signal errors due to noise occur, and the predetermined communication quality is obtained accordingly. Therefore, high CNR characteristics (low noise characteristics) are required. On the other hand, BPSK cannot transmit a larger number of information bits per symbol, but since the phase shift interval is 180 ° and the transmission error due to noise is small, even low CNR characteristics do not affect communication quality.

Therefore, based on the above CNR estimation value, BPSK, which has a small number of information bits that can be transmitted but has few transmission errors, is used in a carrier having a low CNR value, and 16PSK, which has many transmission information bits in a carrier having a high CNR value, is used. Select to improve the transmission rate.

When the CNR value of the carrier is smaller than the predetermined value as a result of the estimation by the SNR estimation unit 26, the communication quality is deteriorated and communication becomes impossible. Therefore, in this case, waste of transmission power is improved. In order to turn off this carrier,
The symbol mapper 11 is controlled via the carrier control unit 27.

Next, the CNR estimation in the CNR estimation unit 26 which characterizes the present invention will be described in detail. FIG. 2 is a functional block diagram showing a configuration example of the CNR estimation unit used in the OFDM communication apparatus according to the present invention. The CNR estimation unit 26 shown in this example sequentially connects the gate circuit 261, which takes out a preamble signal described later from the received OFDM signal and concatenates it to generate an extended preamble signal, the second FFT 262, and the CNR calculation unit 263. A noise power detector 264 is arranged in parallel between the second FFT 262 and the CNR calculation unit 263.

Prior to the description of the operation of the CNR estimation unit 26 shown in FIG. 2, the principle of CNR estimation and a transmission signal configuration example relating to the principle will be described. FIG. 3 is a diagram explaining the principle of this CNR estimation. The same figure (a) is a transmission preamble signal in which a guard interval signal is placed at the beginning, and then a predetermined n-bit fixed data is placed after that, and in the same figure (b) this fixed data is 4 bits (n = 4). Guard interval signal GI
The FFT output signals are shown respectively when is removed. Also, FIGS. 7C and 7D show the signal format and the FFT output signal when two preamble signals of FIG. 9A are connected, respectively.

The number of bits of the fixed data is set so as to match the number of bits that make up the OFDM symbol,
For example, if it is configured with 4 bits, the FFT output signal will be
As shown in, four carrier waves are arranged at intervals of Δf.
On the other hand, when two identical preamble signals are concatenated as shown in (c) of the figure, the number of bits of the signal is doubled to 8 bits. The frequency interval is Δf / 2 as shown in FIG.

At this time, since 4-bit fixed data is repeated, each modulated signal does not change from a constant value on the signal space diagram and is held in an unmodulated state.
(A continuous sinusoidal signal is repeated). As is well known, since such a continuous sine wave signal is observed as a line spectrum, the spectrum spread shown in FIG. 9 (d) does not occur in FIG. 9 (d).

By the way, since the frequencies f0 to f3 generated by the carriers C0 to C3 shown in FIG. 7B are predetermined, the spectra generated at frequencies other than this can be regarded as noise components. However, since noise components (N0, N2, N4, N6) are superimposed on each carrier as shown in FIG. 3D, the observed signals are C0 + N0, C1 + N2, C2 + N4, C3 +. N6, and if each noise component level can be specified (estimated), the level of only the carrier can be specified. Therefore, when the noise level is evaluated as an average noise level, in this example, four noise components, N1, N3, N5, and N7, are observed separately from the carrier wave, so each level is n1, n2, n3, and n4. Then, the average noise level can be evaluated as (n1 + n3 + n5 + n7) / 4 (1).

Therefore, assuming that the noise represented by the equation (1) is superimposed on each carrier, the observation level of each carrier is
The carrier level is estimated by subtracting the average noise level from (C0 + N0, C1 + N2, C2 + N4, C3 + N6). With this, the carrier level and the noise level are calculated, so that the CNR can be estimated.

FIG. 4 is a diagram showing a configuration example of a transmission signal used in the OFDM communication apparatus according to the present invention. In the transmission signal shown in this example, the above-described preamble signal is arranged at the beginning of each frame, and a predetermined number of OFDM symbol data are arranged thereafter.

The operation of the CNR estimation unit 26 shown in FIG. 2 will be described below with reference to FIGS. 3 and 4.
It is assumed that symbol timing synchronization has already been established based on Japanese Patent No. 2772292 or a patent application (Japanese Patent Application No. 2001-201585) filed by the same applicant as the present application.

First, when the transmission OFDM signal shown in FIG. 4 is input to the reception system, the guard signal GI is removed by the guard interval circuit 21 arranged in the preceding stage of the CNR estimation unit 26 and then supplied to the gate circuit 261. It The gate circuit 261 counts the number of input OFDM symbols, takes out a preamble signal for each predetermined count, combines these, and generates an extended preamble signal (see FIG. 4).
Output to 2. As shown in FIG. 3, the frequency spectrum related to this extended preamble signal is transmitted from the FFT 262 to the carrier (C
0 + N0, C1 + N2, C2 + N4, C3 + N6) and noise components (N1, N3, N5, N
7) The noise power detector 264 is output because it is separated into and output.
In (1), the average noise level represented by the above equation (1) is calculated, and the carrier level is calculated in the CNR calculation unit 263 by the procedure described above, and finally the CNR of each carrier is estimated.

In this embodiment, the preamble signal is arranged at the beginning of each frame. In short, it suffices that two or more preamble signals be concatenated to generate an extended preamble signal. You may make it arrange | position a preamble signal to this.

Further, the transmission signal may be configured such that a concatenation of two or more preamble signals from the beginning is arranged at the beginning of each frame. FIG. 5 shows the OFD according to the present invention.
FIG. 11 is a diagram showing another configuration example of a transmission signal used in the M communication device. In the transmission signal shown in this example, two preamble signals are continuously arranged at the beginning of the frame. If such a signal is used, the gate circuit 261 does not need to connect the preamble signals again, so that the processing in the gate circuit 261 becomes light, and therefore the hardware configuration of the gate circuit 261 can be simplified. is there.

If the number of preamble signals forming the extended preamble signal is increased, the accuracy of CNR estimation can be further improved. FIG. 6 shows an OFD according to the present invention.
FIG. 6 is a diagram illustrating an advantage of using an extended preamble signal in which the number of preamble signals is increased to three in the M communication device.
9A shows an extended preamble signal composed of three preamble signals, and FIG. 9B shows an FFT output signal when the guard interval signal GI is removed from the extended preamble signal. In this case,
Since the number of bits of the preamble signal is larger than that shown in FIGS. 3 (c) and (d), the spectrum interval is further narrowed to Δf / 3 due to the nature of the FFT described above, and the number of observable noise components is reduced. To increase.

Here, assuming that the noise power is constant, the spectral levels of the observation noises N0 to N11 are lower than those in FIG. 3 (d). Therefore, each level of the noise components (N0, N3, N6, N9) superimposed on each carrier is also lowered, and the influence of noise level estimation on the carrier is reduced accordingly, so that the accuracy of the CNR estimation value is improved.

Since the OFDM communication apparatus according to the present invention operates as described above, it is possible to select the optimum modulation method according to the CNR characteristics of each carrier, thereby improving the deterioration of communication quality. At the same time, since the carrier wave that cannot be used for communication is not used from the beginning, useless transmission power consumption can be prevented.

When performing the above-mentioned modulation method control and carrier wave OFF control based on the CNR information obtained on the receiving side, it is necessary to inform the transmission partner device of information related to this, and therefore the frame In addition to the above-mentioned preamble signal, required information may be arranged at the head portion (header portion).

[0040]

As described above, according to the present invention, the CNR characteristic related to the transmission path is estimated and the optimum modulation method is selected for each carrier, so that the deterioration of communication quality can be improved.
Further, since the carrier wave that cannot be communicated is not used from the beginning, it is very effective in realizing an OFDM communication apparatus that can reduce waste of transmission power.

[Brief description of drawings]

FIG. 1 is a functional block diagram showing an embodiment of an OFDM device according to the present invention.

FIG. 2 is a functional block diagram showing a CNR estimation unit used in the OFDM device according to the present invention.

FIG. 3 is a diagram illustrating the principle of CNR estimation performed in the OFDM device according to the present invention.

FIG. 4 is a diagram showing a configuration example of a transmission signal used in the OFDM device according to the present invention.

FIG. 5 is a diagram showing another configuration example of a transmission signal used in the OFDM device according to the present invention.

FIG. 6 is a diagram for explaining the advantage of using an extended preamble signal with an increased number of preamble signals in the OFDM device according to the present invention.

FIG. 7 is a functional block diagram showing a configuration example of a conventional OFDM device.

FIG. 8 is a diagram explaining a spectrum of an OFDM signal.

FIG. 9 is a schematic diagram showing a multiplexed waveform of an OFDM signal using 16 carriers.

[Explanation of symbols]

..Symbol mapper 12 ... S / P converter ..High-speed inverse Fourier transformer 14 ... P / S converter ..Sending side guard interval circuit 21..Reception side guard interval circuit 22 ... S / P converter 23..First fast Fourier transformer 24 ... P / S converter ..Symbol demapper 26 ... CNR estimation unit 27..Modulation system / carrier control unit

Claims (5)

[Claims] 1. An extended preamble signal is generated by receiving an OFDM signal having a plurality of preamble signals composed of predetermined fixed data and extracting and concatenating at least two preamble signals from the received signals. Then, by converting this into frequency data by using a Fourier transform means, a carrier component related to the extended preamble signal and other noise components are collectively calculated, and based on this result, the CNR of each carrier component is calculated.
An OFDM communication device characterized by performing estimation. 2. A symbol mapper as at least a transmission system, which disperses transmission data into a plurality of orthogonal carrier waves in which respective frequency components partially overlap with each other and generates a predetermined modulated signal based on a plurality of modulation systems, and the symbol mapper. With an inverse Fourier transform means for multiplexing the modulated signal in the time domain and outputting an OFDM signal, and a Fourier transform means for generating a plurality of orthogonal carrier waves from the received OFDM signal as a receiving system,
OFDM with a symbol demapper that performs a predetermined demodulation process
A communication device, wherein the received OFDM signal has a plurality of preamble signals composed of predetermined fixed data, and at least two or more preamble signals are extracted and concatenated to generate an extended preamble signal. Is converted into frequency data by using a Fourier transform means to collectively calculate a carrier component related to the extended preamble signal and other noise components, and CNR estimation of each carrier component is performed based on this result. An OFDM communication device characterized by the above. 3. The communication control is performed to select a modulation scheme that optimizes a transmission rate of transmission data from the plurality of modulation schemes for each carrier based on a CNR value obtained by the CNR estimation. 2. The OFDM communication device described in 2. 4. The OFDM according to claim 2, wherein when the CNR value obtained by the CNR estimation is lower than a predetermined value, communication control is performed so that the carrier is not used.
Communication device. 5. The extended preamble signal according to claim 1, wherein the plurality of preamble signals are consecutive for a predetermined number, and at least two or more consecutive preamble signals are taken out as an extended preamble signal. 3 or the OFDM according to claim 4
Communication device.